In the fabrication of semiconductor devices, numerous conductive structures, such as gate electrodes, contacts, vias and interconnects, may be formed in or above a substrate, and isolated from one another by one or more dielectric layers. It is often necessary to form openings through the dielectric layers to allow for contact to underlying regions or layers. Generally, an opening through a dielectric layer exposing a diffusion region of a semiconductor substrate or between a gate electrode and a first metal layer are referred to as a “contact opening” or a “contact hole.” An opening through an interlevel dielectric layer is referred to as a “via” or a “via opening.” For purposes of this disclosure, however, “contact opening” may be used to refer to an opening for a contact or via.
After a contact opening has been formed through a dielectric layer, the opening may be cleaned to remove small amounts of debris and residual material formed on surfaces of the contact opening during the contact-etch and to remove a photoresist mask on the surface of the substrate used to pattern the opening.
Conventional post contact-etch clean includes a low temperature dry ash followed by an nitrogen-trifluoride (NF3)/H2 plasma followed by a solvent strip using an organic solvent, such as EKC®-265. The solvent strip is necessary to remove NF3/H2 salts or residue left by the dry clean process. FIG. 1 is a diagram illustrating an electron microscope image of a semiconductor topography formed on a substrate 100 and showing ash residue 102 left in contact openings 104 cleaned according to a conventional method. As seen from this figure, even with the extra solvent strip sub-step, the conventional method is not wholly satisfactory at removing residue left by the dry clean process. In addition to the added cost and the increased cycle or fabrication time of the solvent strip sub-step, the organic solvent leaves residues that cause galvanic corrosion in the contacts leading to unfilled contacts, causing line yield and/or die yield loss. Galvanic corrosion leading to unfilled contacts is particularly a problem with Tungsten (W) contacts. FIG. 2 is a diagram illustrating an electron microscope image of a cross-sectional view of a semiconductor topography formed on a substrate 200, cleaned according to a conventional method, and having an unfilled contact 202. Additional structures shown in the diagram of FIG. 2 include a contact 204 extending from a surface of the substrate to a local interconnect (LI 206), and underlying contacts 208 extending from the LI to underlying elements, regions or contacts (not shown).
Accordingly, there is a need for a post-contact etch clean or cleaning method for cleaning contact openings that substantially eliminates unfilled contacts, thereby significantly improving yield. It is further desirable that the post-contact etch clean reduces processing costs and improves cycle time.
The present invention provides a solution to these and other problems, and offers further advantages over conventional post contact etch cleans.